Microstructural inhomogeneity and magnetic properties in Co-Cr sputtered films

Microstructural inhomogeneity in Co-Cr sputtered films was evaluated by comparing the films' saturation magnetization M s with a Slater-Pauling (S-P) curve for a Co-Cr binary system. The M s deviation from the S-P curve was strongly dependent on sputtering parameters, Ar pressure in particular. Though the radio frequency (RF) power-induced M s deviation from the S-P curve was not so large, it influenced perpendicular coercive force H\min{c}\max{\perp} significantly and was considered to be caused by Cr-rich parts segregated at grain boundaries. Ar pressure also brought about much larger M s deviation from the S-P curve, but did not influence H\min{c}\max{\perp} . When a film was perpendicularly magnetized in a uniform magnetic field, the demagnetizing field acting in the film, deposited under lower Ar pressure, was very close to 4πM. For films deposited under increased Ar pressure, the demagnetizing field decreased, and 4πM-compensation for films went to much excess. It was considered that the M s deviation from the S-P curve occurred due to the existence of two phases, composed of hexagonal close-packed (hcp) and sigma phases, on a Co-Cr binary phase diagram by Hansen. A Cr content of 13 at% was found to be a critical value, only above which M s deviation from the S-P curve occurs in the films. In the less than 13 at% Cr content range, even films exhibited no M s deviation from the S-P curve.